IPS-LCD with a compensation structure for reducing transmittance difference

ABSTRACT

An IPS-LCD with a compensation structure for CD variation. The IPS-LCD panel includes a plurality of pixels wherein each pixel has parallel pixel electrodes and parallel common electrodes positioned such that a respective pixel electrode is disposed adjacent and parallel to a respective common electrode. This panel is characterized in that each spacing between any adjacent common electrode and pixel electrode in one pixel is equal to and different from that of the adjacent pixel.

This application is a Divisional Application of application Ser. No.10/282,027 filed Oct. 29, 2000 now U.S. Pat. No. 6,812,987.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an in-plane switching liquid display(IPS-LCD), more particularly, the present invention relates to anIPS-LCD with a compensation structure for critical dimension (CD)variation.

2. Description of the Related Art

Liquid crystal displays (LCDs) may be classified by the orientation ofthe liquid crystal molecules between the spaced glass substrates. In aconventional twisted nematic LCD (TN-LCD), the liquid crystal moleculesare twisted between the two substrates. In contrast, in an in-planeswitching LCD (IPS-LCD), common electrodes and pixel electrodes areformed on a lower glass substrate (TFT substrate) and an in-planeelectrode field therebetween is generated to rearrange the liquidcrystal molecules along the electrode field. Accordingly, the IPS-LCDhas been used or suggested for improving drawbacks of the conventionalTN-LCD, such as a very narrow viewing angle and a low contrast ratio.

FIGS. 1A and 1B are sectional diagrams of a conventional IPS-LCD, inwhich FIG. 1A shows the alignment of the liquid crystal molecules in anoff state and FIG. 1B shows the alignment of the liquid crystalmolecules in an on state. The IPS-LCD has a lower glass substrate 10, anupper glass substrate 12, and a liquid crystal layer 14 disposed in aspacing between the two parallel glass substrates 10 and 12. On thelower glass substrate 10, serving as a TFT substrate, a plurality ofstrip-shaped common electrodes 16 is patterned on the lower glasssubstrate 10, an insulating layer 18 is deposited on the commonelectrodes 16 and the lower glass substrate 10, and a plurality ofstrip-shaped pixel electrodes 20 is patterned on the insulating layer18.

As shown in FIG. 1A, before an external voltage is applied to theIPS-LCD, the negative liquid crystal molecules 14A are aligned in adirection parallel to the lower glass substrate 10. As shown in FIG. 1B,when an external voltage is applied to the IPS-LCD, an in-plane electricfield is generated between the common electrode 16 and the pixelelectrode 20, resulting in a rotation of the liquid crystal molecules14B toward the in-plane electric field.

Generally, the common electrode 16 and the pixel electrode 20 are formedon the same or different layers and arranged apart from each other by apredetermined distance, known as “spacing”. For example, FIG. 2 shows across-section of a glass substrate having common electrodes and pixelelectrodes thereon. The common electrodes 16 and the pixel electrodes 20have a width of about 4.0 μm. The common electrodes 16 in the edge havea width of about 8.0 μm. Each spacing between a respective commonelectrode 16 and a respective pixel electrode 20 is about 9.0 μm in thesame pixel and the adjacent pixel.

However, critical dimension (CD) variation is easily generated duringformation of the common electrodes 16 and the pixel electrodes 20 causedby many parameters such as different substrate flatness, differentresist thickness, and different etching recipe.

FIG. 3 is a top view showing muras on an IPS-LCD panel caused by CDvariation at area B. The IPS-LCD panel 100 having area A and area B isdisposed in an outer frame 102. A plurality of muras 104, curved spots,are generated on the panel 100 caused by localized CD variation.

Next, FIG. 4 shows a more detailed diagram to explain muras caused by CDvariation and shows a pixel array including area A and area B having CDvariation according to the prior art.

As shown in area A of FIG. 4, the pixel array comprises a plurality ofsmall rectangles having the same numeral (10.00). Each small rectangledenotes one unit pixel that has parallel pixel electrodes 20 andparallel common electrodes 16 positioned such that a respective pixelelectrode 20 is disposed adjacent and parallel to a respective commonelectrode 16. The numeral (10.00) in one small rectangle represents thespacing between any adjacent common electrode 16 and pixel electrode 20.The spacing between any adjacent common electrode 16 and pixel electrode20 in the same pixel is equal to that of the adjacent pixel. Forexample, the spacing between any adjacent common electrode 16 and pixelelectrode 20 is 10.00 μm in the pixel 30.

Turning now to area B of FIG. 4, area B shows a pixel array, havingspacing CD variation of about 0.30 μm. The pixel array comprises aplurality of small rectangles having numeral (10.30) respectively. Eachsmall rectangle denotes one unit pixel that has parallel pixelelectrodes 22 and parallel common electrodes 28 positioned such that arespective pixel electrode 22 is disposed adjacent and parallel to arespective common electrode 28. The numeral (10.30) in one smallrectangle represents the spacing between any adjacent common electrode28 and pixel electrode 22. The spacing between any adjacent commonelectrode 28 and pixel electrode 22 in the same pixel is equal to thatof the adjacent pixel. For example, the spacing between any adjacentcommon electrode 28 and pixel electrode 22 is 10.30 μm in the pixel 40.

FIG. 5 is a three-dimensional diagram showing transmittance differencebetween area A and area B according to the prior art. In FIG. 5, Z-axlerepresents transmittance (%), X-axle and Y-axle mean pixel unit of thepixel array of FIG. 4 including area A and area B.

FIG. 5 shows obvious transmittance difference between area A and area Bso that an observer can perceive the apparent luminance difference.

Therefore, improved IPS-LCD panels formed on an active matrix substratewith a compensation structure for CD variation are needed.

SUMMARY OF THE INVENTION

In view of the above disadvantages, an object of the invention is toprovide an IPS-LCD with a compensation structure for CD variation.According to the IPS-LCD, the transmittance difference between the twopixels can be reduced.

In accordance with one aspect of the invention, there is provided anIPS-LCD with a compensation structure for CD variation. The IPS-LCDcomprises a first substrate; a first pixel, formed on the firstsubstrate, having first parallel pixel electrodes and first parallelcommon electrodes positioned such that a respective pixel electrode isdisposed adjacent and parallel to a respective common electrode; and asecond pixel adjacent to the first pixel, wherein the second pixel hassecond parallel pixel electrodes and second parallel common electrodespositioned such that a respective pixel electrode is disposed adjacentand parallel to a respective common electrode. This LCD is characterizedin that each spacing between any adjacent first common electrode andfirst pixel electrode is equal and has a first distance, each spacingbetween any adjacent second common electrode and second pixel electrodeis equal and has a second distance different from the first distance.Furthermore, the IPS-LCD comprises a second substrate being opposed tothe first substrate and a liquid crystal material being interposedbetween the first substrate and the second substrate.

In accordance with another aspect of the invention, the differencebetween the first distance and the second distance is preferably about0.25*X μm, X=1, 2, 3, or 4. That is to say, the difference between thefirst distance and the second distance is 0.25, 0.50, 0.75 or 1.00 μm.

Furthermore, the first parallel pixel electrodes and the first parallelcommon electrodes are separately formed on the different layers.Otherwise, the first parallel pixel electrodes and the first parallelcommon electrodes can be formed on the same layer.

Furthermore, the first distance and the second distance can be about10.00 μm to 11.30 μm, for example 10.00 μm, 10.25 μm, 10.50 μm, 10.75μm, or 11.00 μm.

In accordance with a further aspect of the invention, there is providedan IPS-LCD with a compensation structure for CD variation. The IPS-LCDcomprises a plurality of pixels wherein each pixel has parallel pixelelectrodes and parallel common electrodes positioned such that arespective pixel electrode is disposed adjacent and parallel to arespective common electrode. This IPS-LCD is characterized in that eachspacing between any adjacent common electrode and pixel electrode in onepixel is equal to and different from that of the adjacent pixel.

In accordance with yet another aspect of the invention, there isprovided an IPS-LCD with a compensation structure for CD variation. TheIPS-LCD comprises a pixel having a plurality of parallel pixelelectrodes and a plurality of parallel common electrodes positioned suchthat a respective pixel electrode is disposed adjacent and parallel to arespective common electrode. This panel is characterized in that eachspacing between any adjacent common electrode and pixel electrode in thepixel is not equal.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the invention is hereinafter described withreference to the accompanying drawings in which:

FIG. 1A is a cross-section showing the alignment of the liquid crystalmolecules in an off state according to the conventional IPS-LCD.

FIG. 1B is a cross-section showing the alignment of the liquid crystalmolecules in an on state according to the conventional IPS-LCD.

FIG. 2 is a cross-section showing a glass substrate having commonelectrodes and pixel electrodes thereon according to the prior art.

FIG. 3 is a top view showing muras on an IPS panel caused by CDvariation at area B.

FIG. 4 is a diagram showing a pixel array including area A and area Bhaving CD variation according to the prior art.

FIG. 5 is a three-dimensional diagram showing transmittance differencebetween area A and area B according to the prior art.

FIG. 6 is a diagram showing a pixel array including area A and area Bhaving CD variation according to the first embodiment of the invention.

FIG. 7 is a three-dimensional diagram showing transmittance differencebetween area A and area B according to the first embodiment of theinvention.

FIG. 8A is a diagram showing a glass substrate having common electrodesand pixel electrodes thereon in one pixel according to the secondembodiment of the invention.

FIG. 8B is a diagram showing a glass substrate having common electrodesand pixel electrodes thereon in another pixel according to the secondembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

FIG. 6 is a diagram showing a pixel array including area A and area Bhaving CD variation according to the first embodiment of the invention.

As shown in area A of FIG. 6, the pixel array comprises a plurality ofsmall rectangles having numerals (10.00, 10.25, 10.50, 10.75, or 11.00)respectively. Each small rectangle denotes one unit pixel that hasparallel pixel electrodes 200 and parallel common electrodes 160positioned such that a respective pixel electrode 200 is disposedadjacent and parallel to a respective common electrode 160. The numeralin one small rectangle represents the spacing between any adjacentcommon electrode 160 and pixel electrode 200. In this embodiment, thespacing between any adjacent common electrode 160 and pixel electrode inthe same pixel is equal to and different from that in the adjacentpixel. For example, the spacing between any adjacent common electrode160 and pixel electrode 200 is 10.25 μm in the pixel 300. The spacingsof the pixels adjacent to the pixel 300 are 11.00 μm, 10.50 μm, 10.00μm, and 10.75 μm respectively. Alternately, the spacing between anyadjacent common electrode 160 and pixel electrode 200 is 11.00 μm in thepixel 310. The spacings of the pixels adjacent to the pixel 310 are10.00 μm, 10.00 μm, 10.25 μm, and 10.25 μm. That is to say, the spacings(10.00 μm, 10.25 μm, 10.50 μm, 10.75 μm, or 11.00 μm) in the pluralityof pixels are randomly arranged. Also, the difference between any twospacings is about 0.25*X μm, X=1, 2, 3, or 4.

Turning now to area B of FIG. 6, area B shows a pixel array, havingspacing CD variation of about 0.30 μm. It is repeated based on area A.The pixel array comprises a plurality of small rectangles havingnumerals (10.30, 10.55, 10.80, 11.05, or 11.30) respectively. Each smallrectangle denotes one unit pixel that has parallel pixel electrodes 202and parallel common electrodes 162 positioned such that a respectivepixel electrode 202 is disposed adjacent and parallel to a respectivecommon electrode 162. The numeral in one small rectangle represents thespacing between any adjacent common electrode 162 and pixel electrode202. In this embodiment, the spacing between any adjacent commonelectrode 162 and pixel electrode in the same pixel is equal to anddifferent from that of the adjacent pixel. For example, the spacingbetween any adjacent common electrode 162 and pixel electrode 202 is10.55 μm in the pixel 400 corresponding to the pixel 300 in area A. Thespacings of the pixels adjacent to the pixel 400 are from 10.00 μm to11.30 μm. For example, the spacings are 11.30 μm, 10.80 μm, 10.30 μm,and 11.05 μm respectively. The spacing between any adjacent commonelectrode 162 and pixel electrode 202 is 11.30 μm in the pixel 410corresponding to the pixel 310 in area A. The spacings of the pixelsadjacent to the pixel 410 are from 10.00 to 11.30 μm. For example, thespacings are 10.30 μm, 10.30 μm, 10.55 μm, and 10.55 μm, respectively.That is to say, the spacings (10.30 μm, 10.55 μm, 10.80 μm, 11.05 μm, or11.30 μm) in the plurality of pixels are randomly arranged. Also, thedifference between any two spacings is about 0.25*X μm, X=1, 2, 3, or 4.

FIG. 7 shows transmittance difference between area A and area Baccording to the first embodiment of the invention. In FIG. 7, Z-axlerepresents transmittance (%), X-axle and Y-axle mean pixel unit of thepixel array of FIG. 6 including area A and area B.

According to the embodiment of the invention, the localizedtransmittance difference between area A and area B with CD variation canbe drastically reduced.

Second Embodiment

FIG. 8A is a diagram showing a glass substrate having common electrodesand pixel electrodes thereon in one pixel according to the secondembodiment of the invention.

In FIG. 8A, the pixel 500 has a plurality of parallel pixel electrodes204 and a plurality of parallel common electrodes 164 positioned suchthat a respective pixel electrode 204 is disposed adjacent and parallelto a respective common electrode 164. The common electrodes 164 have awidth of about 4.0 μm in the central portion and a width of about 8.5 μmin edge portion. The pixel electrodes 204 have a width of about 4.0 μm.Each spacing between any adjacent common electrode 164 and pixelelectrode 204 in the pixel 500 is not equal. The spacings in this pixel500 are respectively 9.25 μm, 9.0 μm, 8.75 μm, 8.5 μm, 8.25 μm, and 8.0μm so that the transmittance in the pixel 500 is variable at differentpositions.

FIG. 8B is a diagram showing a glass substrate having common electrodesand pixel electrodes thereon in another pixel having CD variation inmetal for common electrode.

In FIG. 8B, the pixel 660 has a plurality of parallel pixel electrodes208 and a plurality of parallel common electrodes 166 positioned suchthat a respective pixel electrode 206 is disposed adjacent and parallelto a respective common electrode 166. The common electrodes 166 have awidth of about 3.5 μm (CD variation) in the central portion and a widthof about 8.0 μm in the edge portion. The pixel electrodes 206 have awidth of about 4.0 μm. Each spacing between any adjacent commonelectrode 166 and pixel electrode 206 in the pixel 600 is not equal. Thespacings in this pixel 600 are respectively 9.5 μm, 9.25 μm, 9.0 μm,8.75 μm, 8.5 μm, and 8.25 μm so that the transmittance in the pixel 500is variable at different positions. Therefore, the transmittancedifference between the pixel 500 and pixel 600 with CD variation can bereduced.

While the invention has been described with reference to variousillustrative embodiments, the description is not intended to beconstrued in a limiting sense. Various modifications of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to those skilled in the art upon reference to this description.It is therefore contemplated that the appended claims will cover anysuch modifications or embodiments as may fall within the scope of theinvention defined by the following claims and their equivalents.

1. An IPS-LCD with a compensation structure for CD variation,comprising: at least one pixel having a plurality of parallel pixelelectrodes and a plurality of parallel common electrodes positioned suchthat a respective pixel electrode is disposed adjacent and parallel to arespective common electrode; wherein each spacing between any adjacentcommon electrode and pixel electrode in the pixel is not equal.
 2. AnIPS-LCD with a compensation structure for CD variation as claimed inclaim 1, wherein the spacings are different from each other by adistance of about 0.25*X μm, X=1, 2, 3, or
 4. 3. An IPS-LCD with acompensation structure for CD variation as claimed in claim 1, whereinthe parallel pixel electrodes and the parallel common electrodes areseparately formed on the different layers.
 4. An IPS-LCD with acompensation structure for CD variation as claimed in claim 1, whereinthe spacing is about 10.00 μm to 11.30 μm.